INTRODUCTION TO THE 4C'S

[kong]

ไปเจอมาจาก certifieddiamondsaustralia.com.au
เห็นว่าให้ข้อมูลน่าสนใจดีครับ  เลยเอามาฝาก  เริ่มเลยดีกว่า...

INTRODUCTION TO THE 4C'S
Cut: 

A Diamonds cut is often confused with its shape. Diamonds can be cut into many different types of shapes. However, the cut of a diamond actually refers to its symmetry and proportions.

 A well cut diamond will exhibit a brilliant sparkle. The better a diamonds cut, the more valuable the diamond will become.

The cut is the only aspect of the diamond which is directly influenced by man. All other aspects of the diamond are determined by nature.
 
The diamond cutter always attempts to obtain the best possible cut for each rough diamond crystal. A well cut diamond will display more fire and brilliance. If a diamond is cut too deep or too shallow, it will lose its brilliance and as a result the light will not perform ideally.

A brilliant cut diamond is usually cut with 58 facets and follows specific mathematical formula to which angles are placed in relation to each other.
 
A diamonds cut and proportions are all measured in percentages that are relative to the diameter of the diamonds girdle. The girdle diameter is always set at 100%. The cut, or proportion, of a diamond is measured in percentages relative to the diameter of its girdle. The table and depth percentages are the most important factors in determining the cut of a diamond.

In 1919, a mathematician named Marcel Tolkowsky developed a mathematical formula that calculates the behaviour of light as it passes through a diamond. The diagram above illustrates this formula. This model is still in use today, however it has been slightly modified. The GIA still considers this model whilst grading a diamond for its cut.

Hearts & Arrows

Diamonds of exceptional cut may display the "Hearts and Arrows" effect, which is only viewable through the Hearts and Arrows loupe.

A diamond is only considered to be of Hearts and Arrows quality when it displays perfect, sharp and even hearts and arrows. Many diamonds come close to displaying the hearts and arrows effect, however very few actually show perfect hearts and arrows. A diamond which displays perfect hearts and arrows is very rare and usually will attract a high value.
 

[kong]

Colour:

The best diamond colour is no colour. The most colourless diamond is a D colour diamond which is the most exceptional white. Diamonds are graded from D through to Z.
The grade designated to a diamond depends on the degree in which the diamond shows a hue of colour and as the colour becomes more intense, the colour grade descends down the colour scale. The hue of colour may be yellow, grey or brown in colour.

The colour in diamonds is usually caused by trace elements such as nitrogen that can be present with the diamond crystals structure.

The differences from colour to colour are very minimal and are generally only detectable under laboratory conditions using a certified diamond colour grading set and white light.

GIA and HRD laboratories examine the colour of a diamond in strict laboratory conditions to accurately assign each diamond with its correct colour grade. A laboratory report from GIA or HRD provides the most accurate colour grade for each and every diamond and helps consumers to be able to more easily compare diamonds.

The following diagram illustrates the GIA colour chart, the colour shade shown in this chart is approximate and for illustration purposes only.
 
Fluorescence:
Another phenomenon a diamond may display is fluorescence. This refers to the diamonds ability to fluoresce under ultraviolet (UV) light. Diamonds which show fluorescence usually glow a fluorescent blue colour and sometimes yellow or yellow-green.

Fluorescence is graded by GIA by its intensity as - None, Faint, Medium, Strong or Very Strong. Although it is preferable for a high coloured diamond not to fluoresce, a diamond that is lower in colour (below J) can often look better in appearance if it does show some blue fluorescence.

Fancy Colour:

Fancy coloured diamonds are very rare and highly sort after. Fancy coloured diamonds can be found in pink, yellow, blue, red, orange and green. Fancy coloured diamonds are graded for colour on a different colour scale to the 4C?s colour scale. Fancy diamonds with stronger colour intensity are far greater in value than those with pale fancy colour depending on the hue of colour.

Australia?s Argyle Diamond mine in Western Australia has produced some of the finest pink diamonds ever mined and is the largest supplier of diamonds in the world with the mine producing approximately 30 million carats of diamonds each year. More than 90% of the diamonds produced in the Argyle mine are of gem quality and destined for the jewellery industry.

[kong]

Clarity:



Inclusions are tiny birthmarks of nature present in almost all diamonds. The fewer the inclusions, the more rare and valuable the diamond will become. Most inclusions are not visible to the naked eye and only become apparent using 10 x magnification.
The GIA inclusion grading consists of two factors, internal and external imperfections. Internal imperfections are known as inclusions. External imperfects are known as blemishes.

A clarity grading is assigned to each diamond after assessing it internally and externally using 10 x magnification to identify all the inclusions and blemishes that have been seen. Some diamond reports and certificates will plot exactly where the inclusion and blemishes appear in the diamond and if the inclusion is internal or external. If the report contains a clarity plot, inclusions will be shown in red and blemishes will be shown in green.

In general, the clarity of a diamond does not affect the diamonds visual appearance as most inclusions are not visible to the naked eye. If an inclusion is visible to the naked eye, it will generally be graded as an included diamond (I1, I2 or I3). A clarity grade of SI2 or better on a laboratory report is the point at which inclusions are not apparent to the average naked eye.

We always recommended that you purchase a diamond with the clarity grade of SI2 or better to ensure that the inclusion will not detract from the diamonds visual appearance. It is always more desirable to purchase a diamond that is higher in clarity; however, it is generally very difficult for most people to notice any visible difference in the diamonds appearance. As a diamond?s clarity grade ascends up the scale, the diamonds value increases.

[kong]

Carat:

[

Carat refers to the actual weight of a diamond.
1 Carat = 0.2 grams.

Often diamond weight may be expressed in points. 100 Points is equal to 1 Carat. The table below illustrates therelationship between carat weight and girdle diameter in millimetres. Note that weights may vary depending on the cut and proportions of the actual diamond and the table below is only relevant to brilliant cut diamonds.All girdle diameters are approximate